In many regions of the U.S. and other countries, water resources are limited and privately owned wells are located in places without access to electrical power. Water conservation and preservation of water tables in these regions is important. Furthermore, monitoring of well contents and conditions for regulatory purposes, such as U.S. Geological Service programs and other programs, for example, is becoming increasingly important.
Currently, the water levels in many privately owned wells are not being monitored at all, and many that have been monitored have been monitored manually by the measuring tape or “stick” method. For instance, when a weighted, chalked string or steel tape is lowered into a well, the wetted chalk changes color. Provided that the weighted end of the string or tape is accurately lowered to the floor of the well, the color transition indicates the height of the water level after the string or tape is pulled back out of the well. In contrast, many wells on industrially owned properties and well-funded municipalities and utilities have been monitored by automated systems incorporating hydrostatic head pressure sensors that provide 4-20 mA signal outputs. Compared to these automated systems, the stick method is relatively inaccurate and labor intensive.
One solution for measuring the level of water in a well, U.S. Pat. No. 3,909,948 to Markfelt, is a servo or motorized electromechanical arrangement which measures the running length of cable let out by the servo system, and takes note of two specific positions during runout. The first position is when the sensing element (cable, tape or chain) contacts the top water surface, and the second being, effectively, the well bottom—indicated normally by the sensing element tip reaching the bottom of the well casing. The former position in the prior art system is detected by way of a simple conductivity change between two tip-mounted electrodes, but this detection provides no information besides a visual indication (light a bulb), at which point the user reads the markings on the cable. The latter position is detected by human-sensed line slack, and a similar marking reading.
A seemingly technologically-based system is a product called Pumptec, by Franklin Electric company (see www.franklinelectric.com). Pumtec uses a motor load (current) sensing technique to presumably monitor changing water levels. The product claims include a variety of indications to be inferred from the load, with changes in level being one of them. In fact, the load is so dependent on other factors (even some claiming to be monitored), such as line voltage levels, as to make it impractical as a level indication device. That is, if the pump load decreases due to line voltage drop, there is no way to determine if the “sensed” condition is a voltage drop or a level decrease.
Commercial wells are sometimes monitored by simple systems incorporating well-known hydrostatic head pressure sensors but are impractical for privately owned and remote wells due to expense, size, power requirements, and/or unnecessary and costly industrial control features. U.S. Pat. No. 4,142,411 to Deal discloses a temporarily installed hydrostatic sensor used to determine well draw down. Its purpose is to gather information related to the induced water level error caused by pump action (e.g. the difference between the true water level and localized level in the region of the pump). It may also be used to determine, for diagnostic purposes, the regeneration of the well level. It is not intended to be permanently installed, to provide continuous monitoring, nor is it capable of providing control outputs.
U.S. Pat. No. 3,975,115 to Fisher (assignee Hydrodyne Development Co.) discloses what is usually referred to in industry as a bubbler system, in which compressed air is forced into the water, with the pressure being increased slowly until it just is enough to force all the water out of a submerged tube, and is therefore equal to the hydrostatic pressure exerted by the water. A standard pressure sensing device, outside the well, then infers water level from that pressure reading.
4-20 mA based loops generally offer several advantages over voltage based signaling, such as easier detection of open circuits (from broken wires, for example) and short circuits (from crossed-wires, perhaps) and superior noise rejection characteristics. However, the expense, the complexities of setup, operation, and maintenance of typical 4-20 mA based hydrostatic systems have made them impractical for home owners and owners of wells on larger private properties such as ranches, feed lots, golf course, etc. Moreover, 4-20 mA systems have historically required external electrical power that is either not available or is cost prohibitive with respect to the cost of running electricity to the remote well locations encountered on many private properties.
The need exists for an economical easy-to-use water level monitoring system that will fit within a small pipe or well casings, can be used at remote locations where external power is not available and can provide the user with a display readout of the water level in the well.